Solubility Behavior and Polymorphism of L-Arginine L-Pyroglutamate in Nine Pure Solvents and a Binary Water plus Ethanol System

The solubility data of L-arginine L-pyroglutamate were determined by the static gravimetric method from 283.15 to 323.15 K in nine pure solvents (water, methanol, ethanol, isopropanol, acetone, acetonitrile, dichloromethane, ethyl acetate, and n-hexane) and a water + ethanol binary solvent system. According to experimental results, solubility was positively correlated with temperature. In the selected solvent systems, three different polymorphs denoted as alpha-form, beta-form, and gamma-form were found. In addition, from the data analysis results, the polarity, hydrogen bonding, Hildebrand solubility parameters, and the molecular structure affected the dissolution equilibrium. Two thermodynamic models including the modified Apelblat model and the Yaws model were used to correlate the solubility data. Meanwhile, these models were evaluated by the Akaike information criterion method.